Video games basically comprise a microprocessor utilized as a central processing unit (CPU), a video display control, a memory adapted to store a game program and a video memory for storing picture elements of a video display. The picture elements of a display are addressed and fetched from memory in accordance with the cathode ray tube (CRT) beam location.
In some cases, the system utilizes a full screen memory, that is, a discrete memory address is provided for every discrete display location of the display, either pixel position or line segment position. Such a system is disclosed in U.S. Pat. No. 4,301,503. In another type of system, a pointer indicative of a display location addresses and reads a picture element from a pattern library. Such a system is disclosed in U.S. Pat. No. 4,243,984. A video display procesor (VDP), which together with a dynamic video random access memory (RAM) operates in this manner, is marketed by Texas Instruments as a 9928A video display processor.
To create object movement on the display, in systems using a full screen memory, the addresses of the picture elements are changed periodically, usually during the time of vertical retrace. To create object movement in systems of the second type, the object location in the pointer is changed to a new display location, and the pointer addresses the object in a pattern library at the appropriate beam location.
In either case, the address of the object in the video RAM is changed by the CPU as it receives game player input as to movement of the object. Usually, a game player utilizes a joystick type instrument to control the direction of movement of the object. Such joystick may close switches indicative of coordinate directions of movement. Periodically, the CPU is responsive to the closure condition of the joystick switches. On this particular basis, or some factor thereof, the CPU will rewrite the address of the object in the video RAM. As the address of the object is periodically changed, the object appears to move on the video display in succeeding displays.
In these systems, movement of the object on the screen is at a rate determined by the game program. The object will move a predetermined number of pixels per display frame. There is no known system where rate of movement of an object may be varibly selected or determined by a game player. In some video games, such as disclosed in U.S. Pat. No. 4,114,882, velocity of a moving object is increased as the game continues, at the option of the players, to increase the skill level required. However, the player has no direct control of the velocity of movement of an object.
Also, a video driving game known as TURBO allows some velocity control by positioning an automobile in the horizontal coordinate one pixel per pulse where pulses are generated in accordance with positional movement of a steering wheel, and the steering wheel may be turned at a variable rate. However, this differs from the present invention, where a binary number is generated by counting pulses as a function of a periodic signal, and utilized to control the rate of movement of a video object.
The present invention provides a new dimension in video games in providing a game player with velocity and bi-directional control over an object to be moved on the video screen.